1. Field of the Invention
The present invention relates generally to a wireless power receiver, and more particularly to a wireless power receiver for wirelessly receiving power based on an electromagnetic resonance technique.
2. Description of the Related Art
Mobile terminals such as mobile phones, a Personal Digital Assistant (PDA), etc., are powered by rechargeable batteries, and the battery of the mobile terminal is charged through electrical energy by using a charging apparatus. Generally, a separate contact terminal is located outside of the charging apparatus and the battery, and the charging apparatus and the battery are electrically connected to each other through contact between them.
However, since the contact terminal protrudes outwardly in such a contact type charging scheme, the contact terminal is easily contaminated by foreign substances and thus the battery charging is not correctly performed. Further, battery charging may not be correctly performed in the case in which the contact terminal is exposed to moisture.
Recently, a wireless charging (non-contact) technology has been developed and used for electronic devices to solve the above-mentioned problems.
Such a wireless charging technology employs wireless power transmission/reception, and includes a system in which a battery is automatically charged if the battery is laid on a charging pad without the need to connect the mobile phone to a separate charging connector. The wireless charging technology is currently being used for items such as a wireless electric toothbrush or a wireless electric shaver. Accordingly, a waterproof function is improved since electronic products are wirelessly charged through the wireless charging technology, and the portability of electronic devices is increased since there is no need to provide a wired charging apparatus. Technologies related to wireless charging technology are expected to be significantly developed in the coming age of electric cars.
Wireless charging technology includes an electromagnetic induction scheme using a coil, a resonance scheme using a resonance, and an RF/microwave radiation scheme converting electrical energy to a microwave energy and then transmitting the microwave energy.
A power transmission method through electromagnetic induction corresponds to a scheme of transmitting power between a first coil and a second coil. When a magnet approaches the coil, an induced current is generated. The transmission side generates a magnetic field by using the induced current and a reception side generates energy through an induced current according to changes in the magnetic field. This phenomenon is referred to as magnetic induction, and the power transmission method using magnetic induction has a high energy transmission efficiency.
With respect to the resonance scheme, a system has been developed in which electricity is wirelessly transferred using a power transmission principle of the resonance scheme based on a coupled mode theory even when a device to be charged is several meters from a charging device. A wireless charging system of an MIT team employs a concept in physics that the resonance is the tendency in which when a tuning fork oscillates at a particular frequency, a wine glass next to the tuning fork will oscillate at the same frequency. The research team resonated an electromagnetic wave containing electrical energy instead of resonating sound. The resonated electrical energy is transferred directly only when there is a device having a resonance frequency and parts of electrical energy which are not used are reabsorbed into an electromagnetic field instead of being spread in the air, so that the electrical energy does not affect surrounding machines or people unlike other electromagnetic waves.
According to a resonance scheme, the wireless power receiver includes a rectifying circuit for converting a received Alternating Current (AC) waveform to a Direct Current (DC) waveform and a DC-DC converting circuit for adjusting rectified power in the DC waveform to have a preset voltage value of an output terminal. However, it is difficult to implement the DC-DC converting circuit having a small mounting area while having a high output and efficiency since the DC-DC converting circuit necessarily uses a passive device having a large external parameter. Particularly, when the wireless power receiver is implemented as a mobile communication apparatus such as a mobile phone, an increase in the mounting area has a bad influence on making a device thin overall.
In addition, the DC-DC converting circuit is generally operated in a value less than or equal to than several MHz since the DC-DC converting circuit is an external packaged active device.